I forget how old you are Clod, but it's quite a bit younger than me isn't it?
The best advice I could give you is to go ahead and do it when you're still young enough to cope with the challenges. Once you're knocking on or stepping over the doorway into your 40's, it's so much harder. Not only has your body gotten a bit set in its ways and might rebel against the intrusion as mine has, but your mind is much more set about things too. I find it a lot harder to be fatalistic about some of the more minor things. I over think things at times and just generally seem to be such an old fart in so many ways now. I think if I had my choice again, there's no way i'd have had this latest pregnancy. I think it was a mistake simply because I'm just too old. The risk factors go up exponentially as you would know anyway.
So my suggestion is, do it now or just give it a miss. I don't mean right this second, but some time over the next year or two. I wouldn't worry about age gaps or anything. Those seem to work themselves out pretty well.
I think when it all comes down to it, if you want to have another child, then you should. Money is a factor, but when it comes to bringing a child into a loving home, it's not the be all and end all. Who knows, you might give birth to a future billionaire anyway, so retirement could be very pleasant for you.
I also believe that if you're on the fence about it, it probably means that you want to have another child emotionally, but your logical mind is telling you all the reasons not to. I think the decision you really need to make is whether to be ruled by your heart or you head in this decision. xx